The present invention relates to knitting machines and in particular to means and methods for activating latch needles in knitting machines and monitoring latch needle positions.
Automatic knitting machines use banks of large numbers of closely spaced latch needles to interlock threads in a series of connected loops to produce a knitted fabric. The latch needle is a long flat needle having, at one end, a small hook and a latch that swivels to open and close the hook. The hook ends of the latch needles are moved forwards and backwards towards and away from the threads being knitted into the fabric. As a latch needle is moved, its latch alternately opens and closes so that the hook catches a thread close to it, pulls it to create a loop of fabric, and then releases the thread to start the cycle over again and produce another loop of fabric.
Latch needles are arranged parallel to each other, in arrays of many hundreds to thousands of latch needles in modem knitting machines. The latch needles are placed into narrow latch needle slots that are machined into a planar surface, hereafter referred to as a xe2x80x9cneedle bed surfacexe2x80x9d, of a large rectangular metal plate, hereafter referred to as a xe2x80x9cneedle bedxe2x80x9d. The latch needle slots hold the latch needles in position and confine their motion to linear displacements along the lengths of the latch needle slots. The latch needle slots are parallel to each other and equally spaced one from the other with spacing that varies depending upon the quality and type of fabric being produced. Spacing of two to three millimeters is typical, but spacing significantly less than and greater than two millimeters are also common.
The latch needle slots in a needle bed are sufficiently deep so that all or most of the body of a latch needle lies completely in the latch needle slot in which it is placed and below the needle bed surface into which the latch needle slots are machined. A small square fin that sticks out from one side of the shaft of the latch needle protrudes above the needle bed surface. The fins of all latch needles in a needle bed are accurately aligned in a single straight row perpendicular to the latch needle slots.
The latch needles are moved, hereafter referred to as xe2x80x9cactivatedxe2x80x9d, back and forth in their respective latch needle slots in order to form loops in a fabric being knitted, by a shuttle that travels back and forth along the length of the needle bed surface parallel to the row of aligned latch needle fins. The shuttle has a flat planar surface facing and parallel to the needle bed surface that extends the full length of the shuttle along the direction of travel of the shuttle. The surface has a channel extending the full length of the shuttle along the direction of travel of the shuttle. The channel is open at both of its two ends, and both ends are aligned with the row of aligned fins. As the shuttle moves along the row of latch needle fins, the fins of the latch needles sequentially enter the channel at one end of the channel, travel along the channel length and exit the channel at the other end of the channel. For most of its length the channel is parallel to the row of aligned fins, i.e. the direction of travel of the shuttle, however towards its middle it has a bend. A latch needle is activated when its fin encounters the bend and moves along the direction of the bend. In moving along the direction of the bend, the fin and its latch needle are moved back and forth along the direction of the latch needle slot in which the latch needle is placed, i.e. perpendicular to the row of aligned fins.
The conventional method for moving latch needles in a knitting machine as described above has a number of drawbacks.
For one, the sequential activation of latch needles by a shuttle as the shuttle moves along a needle bed limits the production rates of fabrics. Production rates of fabric produced by knitting machines could be increased if latch needles were individually activated and different combinations of latch needles could be moved simultaneously. Some shuttles in fact have more than one channel in order to simultaneously activate more than one latch needle and increase production rate.
In addition, in the process of knitting a fabric, dust and dirt accumulate in the slots in which latch needles of a knitting machine move. As the dust and dirt accumulate, more force is required to move the latch needles. At some point, dust and dirt accumulate to such an extent that a latch needle jams in its slot. The shuttle is too massive and moves too quickly for it to be practical for the shuttle to be sensitive to, or respond to, changes in the force needed to move a particular latch needle. As the shuttle rushes along the needle bed and encounters a jammed latch needle it breaks the fin or some other part of the jammed latch needle. When this happens physical damage to the knitting machine is often considerably more extensive than the damage to the single latch needle that jammed and knitting machine down time as a result of the damage is prolonged.
In order to prevent damage to knitting machines from jammed latch needles it would be advantageous to have a system for moving latch needles in a knitting machine that activates latch needles individually and is responsive to changes in the forces required to move individual latch needles.
Prior art direct needle drive systems exist that provide for individual activation of latch needles in a knitting machine. These systems, hereafter referred to as xe2x80x9cDNDxe2x80x9d systems, generally provide an actuator for each latch needle and a system for monitoring the position of each latch needle. However, the prior art systems have not been completely satisfactory. The dimensions of actuators used in the prior art systems are large compared to the spacing between latch needles. Complicated spatial configurations are therefore required to pack large numbers of the actuators in a convenient volume of space near to the latch needles in order to couple the actuators to the latch needles.
Additionally, the response times of prior art DND systems are slow. This is the result of slow response times of actuators and of latch needle position monitoring systems used in these systems. The advantages in production rate and decreased knitting machine down time that should be provided by prior art DND systems are at least partly neutralized by the slow response times of these systems.
It is an object of one aspect of the present invention to provide a knitting machine comprising a fast response time DND system for activating latch needles in the knitting machine.
It is an object of another aspect of the present invention to provide a DND system in which each latch needle of a knitting machine is activated exclusively by at least one piezoelectric micromotor which activates only that latch needle.
An object of another aspect of the present invention is to provide a piezoelectric micromotor suitable for use in a fast response time DND system.
An additional aspect of the present invention is to provide a transmission for coupling each latch needle in a DND system, in accordance with a preferred embodiment of the present invention, to an at least one piezoelectric micromotor, which at least one piezoelectric micromotor, hereafter referred to as xe2x80x9cat least one exclusive piezoelectric micromotorxe2x80x9d, is not coupled to any other latch needle.
Piezoelectric micromotors can be made small and powerful and response times of piezoelectric micromotors can satisfy the fast response time requirements of modem knitting machines. The dynamic range of motion available from piezoelectric micromotors and the energy that can be transmitted in short periods of time from piezoelectric micromotors to moveable elements are also consistent with the requirements of modem knitting machines. A piezoelectric micromotor and transmission, in accordance with preferred embodiments of the present invention, can therefore be used to provide fast response time activation of individual latch needles in a kitting machine.
It is an object of yet another aspect of the present invention to provide a DND system comprising a fast response time system for monitoring the position of latch needles activated by the DND system.
It is a further object of another aspect of the present invention to provide an electro-optical latch needle position monitoring system, hereafter referred to as an xe2x80x9cOPMxe2x80x9d, that operates with a fast response time.
DND systems by their nature require fast response time position monitoring systems for monitoring the positions of latch needles that they activate. The positions of the latch needles are controlled in knitting machines to accuracy on the order of 25-50 micrometers (xcexcm). A DND system that moves latch needles with a velocity xe2x80x9cVxe2x80x9d must therefore sample the position of each latch needle it activates with a frequency of between xcx9c2x(Vm/sec÷25 xcexcm) to 2x(Vm/sec÷50 xcexcm), in order to control the position the latch needle to an accuracy of 25 xcexcm-50 xcexcm. It therefore requires a position monitoring system with a response time on the order of (25 xcexcm-50 xcexcm)/2V. In many conventional knitting machines V is on the order of 1.5 m/sec. A DND system that moves latch needles with this velocity therefore requires a system that samples the position of latch needles with a frequency, or sampling rate, of between 50-100 kHz and a response time between 10 xcexcsec and 20 xcexcsec.
Electro-optical systems inherently operate at frequencies that are much faster than typical mechanical cycle frequencies of motion of knitting machine components. In particular an electro-optical OPM, in accordance with a preferred embodiment of the present invention, can provide the fast response time and accuracy of measurement required for monitoring latch needle positions in DND systems.
A piezoelectric micromotor for operating individual latch needles in a DND, in accordance with a preferred embodiment of the present invention, comprises a ceramic vibrator formed in the shape of a thin flat plate having two large planar surfaces and narrow edge surfaces. Piezoelectric vibrators of this type are described in U.S. Pat. No. 5,453,653, which is incorporated herein by reference. The thickness of the vibrator preferably ranges from one to a few millimeters. The thickness of the vibrator thus has dimensions on the order of the size of the spacing between latch needles in a needle bed. It is therefore possible to pack large numbers of these vibrators close to each other with their large planar surfaces parallel and with a thin edge of each vibrator aligned with a single latch needle in the needle bed. Each latch needle is activated (i.e. moved back and forth in its latch needle slot in order to form a loop in a fabric being knitted) by coupling to the latch needle vibratory motion of at least one exclusive piezoelectric micromotor having a thin edge aligned with the latch needle. Coupling of the latch needle and the vibratory motion of the at least one exclusive piezoelectric motor may be accomplished by means of a transmission, in accordance with a preferred embodiment of the present invention.
In a DND, in accordance with a preferred embodiment of the present invention, latch needles in a knitting machine needle bed and piezoelectric micromotors are coupled by a rotary transmission comprising a bearing shaft on which a plurality of annuli is stacked. The annuli rotate freely on the bearing shaft. Each latch needle in the knitting machine needle bed is coupled to vibratory motion of a different at least one exclusive piezoelectric motor via one of the plurality of annuli.
The bearing shaft is mounted over the needle bed, preferably close to the needle bed and with its axis parallel to the needle bed and perpendicular to the latch needle slots in the needle bed. The spacing between the annuli on the shaft is such that the fin of each latch needle in the needle bed is aligned with a different annulus on the bearing shaft. A preferably rigid connecting arm connects the fin of each latch needle in the needle bed to the annulus with which the latch needle fin is aligned. The connecting arm is attached to the fin, preferably by a slideable or flexible joint, formed using methods known in the art.
Each annulus on the bearing shaft is coupled to its own at least one exclusive piezoelectric micromotor, in accordance with a preferred embodiment of the present invention by resiliently pressing the at least one exclusive piezoelectric micromotor against the annulus. Activation of the piezoelectric micromotors coupled to an annulus causes the annulus to rotate. The rotation of the annulus is transmitted to the fin of the latch needle to which the annulus is connected, by the connecting arm. The joint connecting the fin and the connecting arm translates the rotational motion of the connecting arm to a linear motion of the latch needle forwards and backwards in its latch needle slot parallel to the length of the latch needle slot, thereby activating the needle.
In a DND system, in accordance with an alternative preferred embodiment of the present invention latch needles in a knitting machine needle bed and piezoelectric micromotors are coupled by a linear transmission. With the linear transmission each latch needle in a knitting machine needle bed has at least one exclusive piezoelectric micromotor pressed, preferably by resilient force, directly onto the shaft of the latch needle or onto a suitable extension of the shaft of the latch needle. The latch needle slots in which the latch needles are placed, and/or, the surfaces of the needles in contact with the latch needle slots are preferably provided with bearings or nonstick surfaces. This reduces the possibility of a latch needle jamming or sticking in its latch needle slot under the application of the resilient force pressing the at least one exclusive piezoelectric micromotor to the latch needle shaft or suitable extension thereof. Coupled in this way, vibratory motion of the at least one exclusive micromotor pressed to a latch needle shaft or extension thereof activates the latch needle by causing the latch needle to move back and forth in its latch needle slot.
In another form of linear transmission, in accordance with a preferred embodiment of the present invention, piezoelectric micromotors are coupled directly to a xe2x80x9ccouplingxe2x80x9d fin of a latch needle in order to transmit motion to the latch needle. The coupling fin, except for its dimensions, is preferably similar in shape and construction to conventional latch needle fins. The coupling fin is a planar extension of the body of the latch needle having first and second parallel planar sides and thin edges. Preferably, the coupling fin is formed as an integral part of the latch needle and lies in the plane of the body of the latch needle (the latch needle is flat). A rectangular region of the first side and a rectangular region of the second side, hereafter referred to as first and second xe2x80x9ccoupling regionsxe2x80x9d respectively, are preferably clad in wear resistant material suitable for friction coupling with piezoelectric micromotors, such as for example, alumina. Preferably, the first and second coupling regions are congruent and directly opposite each other.
In one configuration for coupling piezoelectric micromotors to the coupling fin, in accordance with a preferred embodiment of the present invention, at least one micromotor is resiliently pressed to each of the first and second coupling regions so that a surface region of the micromotor used for transmitting motion from the micromotor to a moveable element, or a hard wear resistant friction nub on the surface region, contacts the coupling region. Preferably, the same number of piezoelectric micromotors is resiliently pressed to each of the first and second coupling regions. Preferably the at least one micromotor pressed to the first coupling region is identical to the at least one micromotor pressed to the second coupling region. Preferably, points at which the at least one micromotor pressed to the first coupling region contacts the first coupling region and points at which the at least one micromotor pressed to the second coupling region contacts the second coupling region are directly opposite each other. Preferably, the magnitude of the forces exerted on the coupling fin perpendicular to the plane of the coupling fin by the at least one micromotor pressed to the first and second coupling regions are equal. Preferably, the at least one piezoelectric micromotor pressed to each coupling region comprises one micromotor.
The latch needle is driven back and forth in its latch needle slot when the at least one piezoelectric micromotor pressed to the first and second coupling regions are activated so as to transmit linear motion in the same direction to the coupling fin. Preferably, the at least one piezoelectric micromotor pressed to the first and second coupling regions are activated in phase. This substantially prevents a torque that tends to twist the latch needle in its latch needle slot from developing.
In another configuration for coupling piezoelectric micromotors to the coupling fin, accordance with a preferred embodiment of the present invention, a piezoelectric micromotor coupled to a coupling fin is mounted in a transmission bracket. The transmission bracket comprises a bearing or a non-stick surface area against which a surface region of the micromotor used for transmitting motion to a moveable element, or preferably, a wear resistant friction nub on the surface region of the micromotor, is resiliently pressed. In order to couple the piezoelectric micromotor to the coupling fin, the coupling fin is inserted between the friction nub and the bearing or the non-stick surface. With this coupling configuration a single piezoelectric micromotor can be used to activate a latch needle without causing unwanted torque that twists the latch needle in its latch needle slot. Force exerted by the piezoelectric micromotor perpendicular to the plane of the coupling fin is opposed by an equal and opposite force exerted on the coupling fin by the bearing or the non-stick surface.
In order to couple adjacent latch needles in a needle bed to piezoelectric micromotors using coupling fins, in accordance with a preferred embodiment of the present invention, coupling fins of adjacent latch needles are preferably displaced with respect to each other in the direction of motion of the latch needles and/or protrude different distances above the latch needle bed. This provides sufficient space between piezoelectric micromotors coupled to coupling fins of adjacent latch needles so that the piezoelectric micromotors do not interfere with the motion of the latch needles.
A DND system controls latch needle actuators responsive to the position of the particular latch needle to which the actuators are coupled. In a DND system, in accordance with a preferred embodiment of the present invention, latch needle positions are monitored by an OPM.
An OPM, in accordance with a preferred embodiment of the present invention, monitors the position of a latch needle by optically tracking the position of a small light reflecting region, or a region comprising areas of substantially different reflectivity, such as a light reflecting region with a black line, hereafter referred to as a xe2x80x9cfiducialxe2x80x9d, located at a known fixed position on the latch needle. The fiducial is illuminated by light from an appropriately located light source, hereafter referred to as a xe2x80x9cfiducial illuminatorxe2x80x9d. The fiducial reflects a portion of the light from the fiducial illuminator with which it is illuminated into an optical device, hereafter referred to as a xe2x80x9cfiducial imagerxe2x80x9d, comprising a detector having a light sensitive surface. The fiducial imager uses the reflected light to form an image of the fiducial on the light sensitive surface of its detector. A change in the position of the fiducial causes a change in the image of the fiducial on the light sensitive surface, which change is used to determine the change in position of the fiducial.
There are a number of other ways in which the latch needle can be provided with a fiducial, in accordance with preferred embodiments of the present invention. For example, a small retro-reflector can be fixed to a point on the body of the latch needle or an appropriate reflecting discontinuity, such as a scratch or dimple, can be formed on a region of the surface of the latch needle. Preferably, the fiducial reflects incident light diffusely within a cone of half energy angle on the order of 10xc2x0-20xc2x0. The detector and fiducial illuminator comprised in a fiducial imager, in accordance with a preferred embodiment of the present invention, are located so that at any position occupied by the latch needle in its operating range of motion, substantially all the light reflected by the latch needle fiducial into the half energy cone is incident on the detector.
In order to provide position measurements for a plurality of latch needles in a needle bed of a knitting machine, an OPM, in accordance with a preferred embodiment of the present invention, comprises a plurality of fiducial imagers arranged in an array. Preferably, the fiducial imagers are aligned collinearly in a line array defined by an axis that is a straight line. Preferably, the axis is parallel to the needle bed surface of the needle bed and perpendicular to the directions of the needle bed slots.
The number of the plurality of fiducial imagers in the array in a preferred embodiment of the present invention is preferably equal to the number of the plurality of latch needles. Each fiducial imager is aligned with a different one of the plurality of latch needles and provides position data for the latch needle with which it is aligned. The positions of all latch needles in the plurality of latch needles are thus, preferably, simultaneously measurable by the OPM. Preferably, the number of the plurality of latch needles is equal to the number of latch needles in the knitting machine.
In some preferred embodiments of the present invention, the number of the plurality of fiducial imagers in the array of fiducial imagers of an OPM is less than the number of the plurality of latch needles whose positions are to be determined using the OPM. In order to provide position measurements for all the latch needles of the plurality of latch needles, the array of fiducial imagers in the OPM is moved along the needle bed in which the latch needles are held. Preferably, the array of fiducial imagers is moved over the needle bed in a direction collinear with the axis of the array.
In one preferred embodiment of the present invention the fiducial imager comprises a lens and a detector having a light sensitive surface that is divided into first and second regions. The areas of the two regions are preferably equal and preferably abut each other along a straight line. The straight line is preferably oriented substantially perpendicular to the direction of motion of the latch needle. The detector sends first and second signals that are functions of the amounts of reflected light from the fiducial incident on the first and second regions respectively to a controller. The lens focuses reflected light from the fiducial to form an image of the fiducial on the light sensitive surface of the detector. The portions of the image, and thereby the amounts of reflected light, that fall on the first and second regions are different for different positions of the fiducial. The first and second signals, are therefore functions of the position of the fiducial and thereby of the position of the latch needle on which the fiducial is located. The controller uses the first and second signals to determine the position of the latch needle.
In another preferred embodiment of the present invention the fiducial imager comprises a lens, a detector and a light filter. The detector comprises a light sensitive surface sensitive to light in first and second non-overlapping wavelength bands of light. The light filter has first and second filter regions. Each of the filter regions transmits light in a different one of the wavelength bands and does not transmit light in the other wavelength band. The areas of the two filter regions are preferably equal and preferably abut each other along a straight dividing line.
The lens focuses light from the fiducial illuminator that is reflected from the fiducial to form an image of the fiducial on the light sensitive surface of the detector. The filter is positioned with respect to the detector and lens so that the dividing line of the filter and the optic axis of the lens intersect and so that all light from the fiducial focused on the light sensitive surface of the detector passes through the filter. (The filter can also be comprised in an appropriate coating on the lens.) As a result reflected light from the fiducial incident on a first one half of the lens is filtered by the first filter region and reflected light from the fiducial incident on the other half of the lens, a xe2x80x9csecond halfxe2x80x9d, is filtered by the second filter region. Therefore the amounts of light in the image of the fiducial in the first and second wavelength bands are proportional to the amounts of light incident on the first and second halves of the lens respectively.
Preferably, the fiducial illuminator illuminates the fiducial with substantially equal intensities of light in the first and second wavelength bands and the fiducial has substantially the same reflectivity for light in both wavelength bands. Preferably, the transmittance of the first filter region for light in the first wavelength band is substantially equal to the transmittance of the second filter region for light in the second wavelength band. Preferably, intensities registered by the light sensitive surface in the first and second wavelength bands are normalized to the intensities of light radiated by the fiducial illuminator in the first and second wavelength bands. The intensities are preferably corrected for differences in reflectivity of the fiducial in the two wavelength bands. Preferably, the intensities are corrected for differences between the transmittance of the first filter region for light in the first wavelength band and the transmittance of the second filter region for light in the second wavelength band. The intensities are preferably corrected for differences in sensitivity of the light sensitive surface to light in the two wavelength bands.
Hereinafter, when intensities, integrated intensities or amounts of light on light sensitive surfaces are compared, it is understood that they are appropriately normalized to the intensity of light radiated by the fiducial illuminator and corrected for biases introduced by various optical components.
The amounts of light incident on the first and second halves of the lens are functions of the position of the fiducial. When the fiducial is located on the optic axis of the lens the first and second halves of the lens receive the same amounts of reflected light. When the fiducial is displaced from the optic axis in the direction of one or the other halves of the lens, the half towards which the fiducial is displaced gets more light and the other half gets less light. Preferably, the dividing line of the filter is substantially perpendicular to the motion of the latch needle and thereby to the fiducial in order to maximize change in the amounts of light incident on the first and second halves of the lens with change of position of the fiducial. The first and second signals sent by the detector to the controller are therefore functions of the position of the fiducial. These signals are used by the controller to determine the position of the fiducial and the latch needle on which the fiducial is located.
In an alternate preferred embodiment of the present invention, the fiducial imager comprises two preferably identical light detectors, each having its own lens that focuses an image of the fiducial onto the detector""s light sensitive surface. The two light detectors are displaced from each other by a short distance. The line between the two detectors is aligned parallel with and in the plane of the latch needle slot of the latch needle whose position the detectors are used to determine. The difference between the amounts of light from the fiducial illuminator that is reflected into each of the two detectors is different for different positions of the latch needle along the latch needles range of motion. For example, assume the fiducial illuminator is equidistant from both detectors. When the fiducial is equidistant from both detectors each detector receives the same amount of reflected light from the fiducial and the difference between the amounts of light received by the detectors is substantially zero. If the fiducial is displaced along the direction of motion of the latch needle towards one of the detectors, the detector towards which it is displaced receives an increased amount of reflected light and the other detector receives a decreased amount of light. The difference between the amounts of reflected light received by the detectors from the fiducial is a function of the displacement of the fiducial from the position of the fiducial at which both detectors receive the same amount of reflected light. This difference, and thereby the location of the fiducial and the latch needle, is determined by a circuit that receives an input signal from each detector that is a function of the intensity of light incident on the detector.
In another preferred embodiment of the present invention the fiducial imager comprises one light detector and two lenses. The light sensitive surface of the light detector is sensitive to light in two non-overlapping wavelength bands of light. The fiducial illuminator illuminates the fiducial with preferably equal intensities of light from both wavelength bands. Each of the lenses transmits light in only one of the two different wavelength bands. Both lenses focus light reflected from the fiducial onto the light sensitive surface of the detector. The lenses are displaced a short distance from each other and the line connecting the centers of the lenses is aligned parallel with and in the plane of the latch needle slot of the latch needle whose position the fiducial imager is used to determine. As in the previous fiducial imager, when the fiducial is equidistant from both lenses the detector registers equal intensity (appropriately normalized as discussed above) of light in both of the wavelength bands for which it is sensitive. As the fiducial is displaced towards one or the other of the lenses, the difference between the intensities of light registered by the detector in the two wavelength bands changes as a function of the amount of the displacement.
In a yet another preferred embodiment of the present invention, the fiducial imager comprises one light detector and a lens. The light sensitive surface of the light detector is sensitive to light in two non-overlapping wavelength bands of light. The lens transmits light in both of the two wavelength bands. The latch needle whose position is measured using the fiducial imager is provided with two fiducials displaced from each other by a short distance along the length of the latch needle. Each of the fiducials reflects light in a different one of the wavelength bands to which the detector is sensitive and absorbs light in the other wavelength band. The lens focuses both fiducials on the light sensitive surface of the light detector. The difference between the light intensity registered by the detector in the two different wavelength bands is used to determine the position of the two fiducials and thereby of the latch needle.
In still yet another preferred embodiment of the present invention, the fiducial imager comprises a monochromatic light detector having a pixelated light sensitive surface, such as a CCD, and a lens that focuses an image of the fiducial on the pixelated surface. The location of the fiducial image on the pixelated surface is determined to be the center of gravity of the illumination pattern on the surface that is caused by the fiducial image. The location of the center of gravity is determined to sub-pixel resolution from the locations of pixels illuminated by the fiducial image and the intensities with which these pixels are illuminated using techniques known in the art. The position of the fiducial and its latch needle is determined from the location of the fiducial image on the pixelated surface by techniques that are well-known in the art.
It should be realized that an OPM, in accordance with a preferred embodiment of the present invention, is useable for any application requiring position monitoring of latch needles and its use is not restricted for use only in cooperation with a DND system. It should also be realized that an OPM, in accordance with a preferred embodiment of the present invention, is useable for providing latch needle position measurements for a DND system irrespective of the type of actuators used to activate latch needles in the DND system, and is not limited to use with DND systems that use piezoelectric micromotors or actuators.
There is therefore provided in accordance with a preferred embodiment of the present invention an optical position monitor for determining the position of a latch needle in a knitting machine comprising: at least one fiducial at a known fixed location on the body of the latch needle; a fiducial imager that produces at least one optical image of the at least one fiducial on at least one light sensitive surface, wherein the at least one optical image changes with changes in position of the at least one fiducial; and a controller that receives at least one signal responsive to the changes in the at least one image and uses the at least one signal to determine the position of the at least one fiducial and thereby of the latch needle.
Preferably, the optical position monitor comprises at least one fiducial illuminator that illuminates the at least one fiducial. Additionally or alternatively, the changes in the at least one image comprise changes in integrated intensity of the at least one image. Alternatively or additionally, the at least one fiducial comprises a single fiducial.
In some preferred embodiments of the present invention the at least one light sensitive surface comprises first and second light sensitive surfaces and the at least one signal comprises first and second signals responsive to the intensity of light reflected by the at least one fiducial imaged on the first and second light sensitive surfaces respectively.
Preferably, the first and second light sensitive surfaces comprise first and second contiguous light sensitive surfaces. The at least one image preferably comprises a single image having first and second portions on the first and second light sensitive surfaces respectively and the ratio between the first and second portions depends upon the position of the at least one fiducial.
Alternatively, the first and second light sensitive surfaces comprise first and second light sensitive surfaces that are preferably displaced from each other by a distance. Preferably, the optical position monitor comprises first and second lenses and the at least one image comprises first and second images, wherein the first and second light sensitive surfaces are optically aligned with the first and second lenses respectively, and the first lens produces the first image on the first light sensitive surface and the second lens produces the second image on the second light sensitive surface and wherein the ratio between the integrated intensities of the first and second images depends upon the position of the at least one fiducial.
In still other preferred embodiments of the present invention the at least one light sensitive surface comprises a single light sensitive surface sensitive to light in first and second non-overlapping wavelength bands of light and the at least one signal comprises first and second signals responsive to the integrated intensity of light incident on the single light sensitive surface in the first and second wavelength bands respectively.
Preferably, the optical position monitor comprises a light filter having first and second filter regions wherein the first region transmits light only in the first wavelength band and the second filter region transmits light only in the second wavelength band and light reflected from the single fiducial that is imaged on the light sensitive surface, passes through either the first filter region or the second filter region.
Preferably, the at least one image comprises a single image, wherein a first portion of light in the single image reflected from the fiducial passes through the first filter region and a second portion of light in the single image reflected from the fiducial passes through the second filter region, and wherein the ratio between first and second portions depends upon the position of the fiducial.
Alternatively, the optical position monitor comprises a first lens and a second lens displaced from each other by a distance, wherein the first lens transmits light only in the first wavelength band and the second lens transmits light only in the second wavelength band, wherein the first and second lenses produce first and second images of the fiducial on the light sensitive surface respectively, and the relative integrated intensity of light in the first and second images is a function of the position of the fiducial.
In some preferred embodiments of the present invention the at least one fiducial comprises at least a first and a second fiducial. Preferably, the at least one light sensitive surface comprises a single light sensitive surface sensitive to light in first and second non-overlapping wavelength bands of light and wherein the at least one signal comprises first and second signals responsive to the integrated intensity of light incident on the single light sensitive surface in the first and second wavelength bands respectively. Preferably, the first fiducial reflects light only in the first wavelength band and the second fiducial reflects light only in the second wavelength band, and the optical position monitor comprises: a lens that produces a first image of the first fiducial and a second image of the second fiducial on the light sensitive surface using light reflected from the first and second fiducials respectively; wherein the integrated intensity of light in the first and second images depends upon the position of the first and second fiducials.
In an optical position monitor in accordance with some preferred embodiments of the present invention, changes in the at least one image comprise changes in the location of the at least one image on the at least one light sensitive surface. Preferably, the at least one light sensitive surface comprises at least one pixelated surface. Preferably, the at least one signal comprises signals responsive to the intensity of light incident on each pixel of the at least one pixelated surface. The at least one image preferably comprises a single image on each of the at least one pixelated surface. In some preferred embodiments of the present invention the at least one pixelated surface comprises a single pixelated surface.
In some preferred embodiments of the present invention a location for each of the at least one image is defined as the location of an optical center of gravity of the at least one image, which location is determined from the signals responsive to the intensity of light incident on each pixel of the at least one pixelated surface, and wherein the location of the optical center of gravity is responsive to the position of the at least one fiducial.
In some preferred embodiments of the present invention wherein changes in the at least one image comprise changes in the location of the at least one image on the at least one light sensitive surface, the at least one fiducial comprises a single fiducial.
In some preferred embodiments of the present invention the single fiducial of a plurality of latch needles is imaged on different regions of the at least one pixelated surface, and the optical position monitor is used to determine the positions of a plurality of latch needles. Preferably, the number of the plurality of latch needles is greater than 5. Alternatively, the number of the plurality of latch needles is preferably greater than 10. Alternatively, the number of the plurality of latch needles is preferably greater than 20.
In some preferred embodiments of the present invention an optical position monitor comprises a means for selectively aligning the optical position monitor with different latch needles in the needle bed.
There is further provided an optical position monitor for simultaneously monitoring the position of a plurality of latch needles in a knitting machine needle bed, which needle bed has a plane surface having latch needle slots that are parallel to each other, comprising a plurality of optical position monitors in accordance with a preferred embodiment of the present invention.
Preferably, each of the plurality of the optical position monitors is aligned with a different latch needle and is used to determine the position of at least the latch needle with which it is aligned.
The optical position monitors in the plurality of optical position monitors are preferably aligned in a line array along a straight line. Preferably, the line array is parallel to the needle bed surface and perpendicular to the latch needle slots. Alternatively or additionally, the spacing between an optical position monitor in the line array and an adjacent optical position monitor is the same for any optical position monitor in the line array. Preferably, the spacing is equal to the spacing between adjacent latch needles of the plurality of latch needles.
In some preferred embodiments of the present invention, the number of the plurality of needles is equal to the number of needles in the needle bed.
In other preferred embodiments of the present invention the number of the plurality of latch needles is less than the number of needles in the needle bed and the optical position monitor includes a means for selectively aligning the optical position monitor with different groups of latch needles in the needle bed. Preferably the means for aligning the optical position monitor with different groups of latch needles comprises means for translating the optical position monitor in a direction parallel to the needle bed and perpendicular to the latch needle slots.
In some preferred embodiments of the present invention the optically reflective fiducial comprises at least two regions on the surface of the latch needle having different reflectivities. Preferably, at least one of the at least two regions comprises a retroreflector. Alternatively or additionally, at least one of the at least two regions comprises at least one discontinuity in the surface of the latch needle. Preferably, the at least one discontinuity comprises at least one straight line groove on the surface of the latch needle. Alternatively or additionally, the discontinuity preferably comprises at least one dimple depressed into the surface of the latch needle. Alternatively or additionally, at least one of the at least two regions is preferably substantially non-reflecting.
Additionally or alternatively, light reflected from the fiducial is substantially confined within a cone of half energy angle less than 20xc2x0. Additionally or alternatively light reflected from the fiducial is substantially confined within a cone of half energy angle less than 15xc2x0. Additionally or alternatively, light reflected from the fiducial is substantially confined within a cone of half energy angle less than 10xc2x0.
There is further provided an actuator system for activating a latch needle, which latch needle has a shaft, comprising: a flat planar extension of the shaft having first and second parallel planar surfaces; at least one piezoelectric micromotor having a first surface region for transmitting motion to a moveable element, which first surface region is resiliently pressed to the first surface and at least one additional piezoelectric motor having a second surface region for transmitting motion to a moveable element which second surface region is resiliently pressed to the second surface; and wherein vibratory motions of the first and second surface regions apply forces to the flat extension that cause motion in the latch needle.
There is also provided an actuator system for activating a latch needle, which latch needle has a thin flat shaft comprising: a flat planar extension of the shaft having first and second planar surfaces; a piezoelectric micromotor having a surface region for transmitting motion to a moveable element; a transmission bracket for holding the piezoelectric micromotor, the transmission bracket comprising a bearing surface and a means for resiliently urging the surface region of the piezoelectric micromotor towards the bearing surface; and wherein the flat extension is inserted between the surface region of the piezoelectric micromotor and the bearing or the non-stick surface and wherein vibratory motion of the surface region applies force to the flat extension causing motion in the latch needle.
Preferably, the bearing surface is the surface of a rotatable roller or ball. Alternatively or additionally, the bearing surface is a surface having a low friction coating.
In an actuator system for activating a latch needle according to some preferred embodiments of the present invention, the surface region for transmitting motion to a moveable element comprises a wear resistant nub that makes contact with a surface of the moveable element towards which the surface region for transmitting motion is resiliently pressed in order to transmit motion to the moveable element.
In an actuator system for activating a latch needle according to some preferred embodiments of the present invention, points on surfaces of the flat extension at which said surface regions of the piezoelectric micromotors make contact are clad in wear resistant material.